Extra virgin is the top grade of olive oil: mechanically extracted, no defects, and free acidity of 0.8 percent or less. Below it sit virgin, then refined oils sold as pure, light or simply olive oil, and finally pomace oil at the bottom. Here is what each grade actually means, so you know what you are buying and drinking.
The quick hierarchy
From best to lowest: extra virgin olive oil, virgin olive oil, refined oils sold as olive oil, pure or light, and olive pomace oil. Only the first two are unrefined and made by mechanical means alone.
Extra virgin olive oil
The gold standard. Made purely mechanically, with no heat or chemicals, free acidity of 0.8 percent or less, and no taste or aroma defects. It keeps the natural polyphenols and flavour, which is why it is the only grade worth drinking. The best sit well below the acidity limit, around 0.2 to 0.4 percent.
Virgin olive oil
Also mechanically extracted and unrefined, but a step down: free acidity up to 2.0 percent is allowed, along with minor flavour defects. Perfectly good oil, just not the top tier, and less peppery and polyphenol-rich than extra virgin.
Refined, pure and light
When virgin oil is defective, it is refined using heat and chemical processing to strip out the faults, leaving a neutral, almost flavourless oil low in polyphenols. This is then blended with a little virgin oil and sold as olive oil or pure olive oil. Light and extra light are the same refined product marketed on their pale colour and mild taste. Crucially, light does not mean fewer calories, as all olive oil has about 120 calories a tablespoon.
Olive pomace oil
The lowest grade. Solvents extract the last of the oil from the pomace, the pulp and stones left after pressing, and it is then refined and blended with a touch of virgin oil. Cheap and neutral, it suits high-heat cooking, not drinking.
What is free acidity?
Free acidity is the percentage of free oleic acid in the oil, and it is one of the clearest quality markers. Lower means the fruit was sound and pressed promptly. Extra virgin must be 0.8 percent or below, and the finest oils are far lower.
Which grade should you buy?
For drinking and for finishing food raw, always extra virgin. For understanding how it is made, see cold pressed vs heat extracted olive oil, and to choose one to drink, read the best olive oil to drink or start with can you drink olive oil, and which one to choose.
